[PATCH v5 0/5] mm: Unconditional per-VMA locks and cleanups

COLD40d

Revision v5 of 5 in this series.

8 messages, 2 authors, 2026-08-12 · open the first message on its own page

[PATCH v5 0/5] mm: Unconditional per-VMA locks and cleanups

From: Suren Baghdasaryan <surenb@google.com>
Date: 2026-08-12 01:11:06

v2 version of this patchset [1] was written by Dave Hansen and per his
request, I'm taking over this series.

tl;dr: Make per-VMA locks available in all configs. Simplify some
of the per-VMA lock users now that they can rely on them being
always available.

Binder and networking folks: Your code is the target of the cleanups.
I'm cc'ing you now on v2 because there's emerging consensus on the mm
side that the approach here is sane. I'm not quite sure how this pile
would get merged, but ack/review tags would be appreciated if this
looks good to you.

Longer version:

When working on some x86 shadow stack code, it was a real pain to
avoid causing recursive locking problems with mmap_lock. One way
to avoid those was to avoid mmap_lock and use per-VMA locks instead.
They are great, but they are not available in all configs which
makes them unusable in generic code, or if you want to completely
avoid mmap_lock.

Make per-VMA locks available in all configs. Right now, they are
only available on select architectures when SMP and MMU are enabled.
But all of the primitives that per-VMA locks are built on (RCU, maple
trees, refcounts) work just fine without SMP or MMU.

The only real downside is that making VMAs a wee bit bigger on !MMU
and !SMP builds.

The upside is much cleaner code, lower complexity and less #ifdeffery.

Clean up a binder VMA locking site now that it can rely on per-VMA
locks.

Building on top of universally-available per-VMA locks, introduce a
new helper. Since the new API does not require callers to have a
fallback to mmap_lock, it's much easier to use. Callers can
potentially replace this very common kernel idiom:

	mmap_read_lock(mm);
	vma = vma_lookup()
	// fiddle with vma
	mmap_read_unlock(mm);

with:

	vma = vma_start_read_unlocked(mm, address);
	// fiddle with vma
	vma_end_read(vma);

Which avoids mmap_lock entirely in the fast path.

Use that new API for another binder site and one in the TCP code.

Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: "Liam R. Howlett" <redacted>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: linux-mm@kvack.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Todd Kjos <tkjos@android.com>
Cc: Christian Brauner <christian@brauner.io>
Cc: Carlos Llamas <cmllamas@google.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: David Ahern <dsahern@kernel.org>
Cc: netdev@vger.kernel.org

Changes from v4 [2]:
Patch 1:
- Changed vma_assert_locked() NOMMU implementation to assert ma->vm_mm is
  locked, per Sashiko
- Amended patch 1 changelog to include vma_start_read_locked() and
  lock_vma_under_rcu in NOMMU considerations section, per Lorenzo Stoakes
- Changed comments for stack_map_lock_vma(), per Matthew Wilcox
- Added early exit in lock_vma_under_rcu() for !CONFIG_MMU,
  per Lorenzo Stoakes
Patch 2:
- Updated changelog to explain the extra change making missing VMA
  handling consistent, per Carlos Llamas
Patch 3:
- Rewrote changelog to better represent the changes in the patch,
  per Matthew Wilcox
Patch 5:
- Fixed vma_start_read_unlocked() function name in the changelog,
  per Matthew Wilcox
All patches
- Added Acked-by and Reviewed-by, per Vlastimil Babka, Lorenzo Stoakes and
  Alice Ryhl
- Rebased over mm-unstable, per Lorenzo Stoakes

Applies cleanly over mm-unstable

[1] https://lore.kernel.org/all/20260610230409.A44D29FA@davehans-spike.ostc.intel.com/
[2] https://lore.kernel.org/all/20260806200548.3124802-1-surenb@google.com/

Dave Hansen (5):
  mm: Make per-VMA locks available universally
  binder: Make shrinker rely solely on per-VMA lock
  mm: Add RCU-based VMA lookup helper that waits for writers
  binder: Remove mmap_lock fallback
  tcp: Remove mmap_lock fallback path

 arch/arm/Kconfig                       |  1 -
 arch/arm64/Kconfig                     |  1 -
 arch/loongarch/Kconfig                 |  1 -
 arch/powerpc/platforms/powernv/Kconfig |  1 -
 arch/powerpc/platforms/pseries/Kconfig |  1 -
 arch/riscv/Kconfig                     |  1 -
 arch/s390/Kconfig                      |  1 -
 arch/x86/Kconfig                       |  2 -
 drivers/android/binder/page_range.rs   | 19 +-----
 drivers/android/binder_alloc.c         | 62 +++++++----------
 fs/proc/internal.h                     |  2 -
 fs/proc/task_mmu.c                     | 93 -------------------------
 include/linux/mm.h                     | 12 ----
 include/linux/mm_types.h               |  8 +--
 include/linux/mmap_lock.h              | 94 +++++++++++---------------
 kernel/bpf/stackmap.c                  | 17 ++---
 kernel/bpf/task_iter.c                 |  2 +-
 kernel/fork.c                          |  2 -
 mm/Kconfig                             | 12 ----
 mm/Kconfig.debug                       |  1 -
 mm/debug.c                             |  4 --
 mm/init-mm.c                           |  2 -
 mm/memory.c                            |  2 -
 mm/mmap_lock.c                         | 61 ++++++++++-------
 mm/pagewalk.c                          |  2 -
 mm/rmap.c                              |  2 -
 mm/userfaultfd.c                       | 61 ++---------------
 net/ipv4/tcp.c                         | 31 +++------
 rust/kernel/mm.rs                      | 57 ++++++++++------
 tools/testing/vma/include/dup.h        |  5 +-
 tools/testing/vma/vma_internal.h       |  1 -
 31 files changed, 166 insertions(+), 395 deletions(-)


base-commit: 1029098ee3275ea5b78e329ce132262affa2f8cc
-- 
2.55.0.691.gc56d675ccc-goog

[PATCH v5 1/5] mm: Make per-VMA locks available universally

From: Suren Baghdasaryan <surenb@google.com>
Date: 2026-08-12 01:11:09

From: Dave Hansen <dave.hansen@linux.intel.com>

The per-VMA locks have been around for several years. They've had some
bugs worked out of them and have seen quite wide use. However, they
are still only available when architectures explicitly enable them.
Remove the conditional compilation around the per-VMA locks, making
them available on all architectures and configs.

The approach up to now seemed to be to add ARCH_SUPPORTS_PER_VMA_LOCK
when the architecture started using per-VMA locks in the fault
handler. But, contrary to the naming, the Kconfig option does not
really indicate whether the architecture supports per-VMA locks or
not. It is more of a marker for whether the architecture is likely to
benefit from per-VMA locks.

To me, the most important thing side-effect of universal availability
is letting per-VMA locks be used in SMP=n configs. This lets us use
per-VMA locking in all x86 code without fallbacks.

Overall, this just generally makes the kernel simpler. Just look at
the diffstat. It also opens the door to users that want to use the
per-VMA locks in common code. Doing *that* brings additional
simplifications.

The downside of this is adding some fields to vm_area_struct and
mm_struct. There are likely ways to optimize this, especially for
things like SMP=n configs. For now, do the simplest thing: use the
same implementation everywhere.

== Considerations for NOMMU config ==

NOMMU systems do not write-lock VMAs, therefore read-locking a VMA
would always succeed unless VMA is detached. Therefore for NOMMU
config we make vma_mark_attached() a NOOP, which keeps VMAs always in
detached state. This causes VMA read-locking to always fail and the
caller falls back to locking mmap_lock.

The following functions will have a different implementation in NOMMU
config:

- vma_mark_attached(), vma_mark_detached() are made NOOPs, keeping VMAs
always in a detached state and preventing assertions and refcount
underflows;

- vma_start_write(), vma_start_write_killable() are made NOOPs to avoid
warnings in __vma_start_write() due to VMAs being detached.
These functions are not used in NOMMU code but __vma_start_write()
is an exported function, therefore might be used by drivers.

- vma_assert_attached() is made NOOP because it's reachable from NOMMU
code via split_vma()->vma_iter_store_new()->vma_iter_store_overwrite();

- vma_assert_write_locked() is asserting vma->vm_mm is write-locked, as
was done before this change;

- vma_assert_locked() is asserting vma->vm_mm is locked, as was done
before this change;

The following functions work for both MMU and NOMMU configs:

- vma_lock_init() performs the same initialization as for MMU config;

- mm_lock_seqcount_init(), mm_lock_seqcount_begin(), mm_lock_seqcount_end()
are called from mmap_write_{lock|unlock} and update mm_lock_seq correctly.

- mmap_lock_speculate_try_begin(), mmap_lock_speculate_retry() work as is
because mm_lock_seq is updated correctly;

- vma_start_read(), vma_start_read_locked() will always fail because VMAs
are always detached;

- vma_end_read() will never be called because vma_start_read() never
succeeds;

- vma_is_attached() always return false because VMAs are always detached;

- vma_assert_detached() will never trigger because VMAs are never attached;

- vma_start_read_locked() always return false because VMAs are always
detached;

- lock_vma_under_rcu() will be safe as the attempted read lock will bail;

Changes in the following files are not affecting NOMMU config:

task_mmu.c - not compiled when CONFIG_MMU=n;
pagewalk.c - not compiled when CONFIG_MMU=n;
userfaultfd.c - not compiled when CONFIG_MMU=n (CONFIG_USERFAULTFD depends
on CONFIG_MMU);

The following changes in the BPF code are made to keep NOMMU config
working like before:

stack_map_lock_vma() - keeps mmap_lock in NOMMU config;
bpf_iter_task_vma_new() - bails out in NOMMU config;

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Liam R. Howlett <redacted>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: linux-mm@kvack.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Todd Kjos <tkjos@android.com>
Cc: Christian Brauner <christian@brauner.io>
Cc: Carlos Llamas <cmllamas@google.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Ahern <dsahern@kernel.org>
Cc: netdev@vger.kernel.org
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 arch/arm/Kconfig                       |  1 -
 arch/arm64/Kconfig                     |  1 -
 arch/loongarch/Kconfig                 |  1 -
 arch/powerpc/platforms/powernv/Kconfig |  1 -
 arch/powerpc/platforms/pseries/Kconfig |  1 -
 arch/riscv/Kconfig                     |  1 -
 arch/s390/Kconfig                      |  1 -
 arch/x86/Kconfig                       |  2 -
 fs/proc/internal.h                     |  2 -
 fs/proc/task_mmu.c                     | 93 --------------------------
 include/linux/mm.h                     | 12 ----
 include/linux/mm_types.h               |  8 +--
 include/linux/mmap_lock.h              | 75 +++++++--------------
 kernel/bpf/stackmap.c                  | 17 ++---
 kernel/bpf/task_iter.c                 |  2 +-
 kernel/fork.c                          |  2 -
 mm/Kconfig                             | 12 ----
 mm/Kconfig.debug                       |  1 -
 mm/debug.c                             |  4 --
 mm/init-mm.c                           |  2 -
 mm/memory.c                            |  2 -
 mm/mmap_lock.c                         | 26 +------
 mm/pagewalk.c                          |  2 -
 mm/rmap.c                              |  2 -
 mm/userfaultfd.c                       | 55 ---------------
 rust/kernel/mm.rs                      | 32 +++------
 tools/testing/vma/include/dup.h        |  5 +-
 tools/testing/vma/vma_internal.h       |  1 -
 28 files changed, 48 insertions(+), 316 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 9187240a02db..f815209167cd 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig

@@ -41,7 +41,6 @@ config ARM
 	select ARCH_SUPPORTS_ATOMIC_RMW
 	select ARCH_SUPPORTS_CFI
 	select ARCH_SUPPORTS_HUGETLBFS if ARM_LPAE
-	select ARCH_SUPPORTS_PER_VMA_LOCK
 	select ARCH_SUPPORTS_RT
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 11a9c534b7b4..21eb64b24a2c 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig

@@ -81,7 +81,6 @@ config ARM64
 	select ARCH_HAS_PTE_PROTNONE
 	select ARCH_SUPPORTS_NUMA_BALANCING
 	select ARCH_SUPPORTS_PAGE_TABLE_CHECK
-	select ARCH_SUPPORTS_PER_VMA_LOCK
 	select ARCH_SUPPORTS_HUGE_PFNMAP if TRANSPARENT_HUGEPAGE
 	select ARCH_SUPPORTS_RT
 	select ARCH_SUPPORTS_SCHED_SMT

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index e20acbe5fe7b..7741e39eca2b 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig

@@ -69,7 +69,6 @@ config LOONGARCH
 	select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
 	select ARCH_HAS_PTE_PROTNONE if 64BIT
 	select ARCH_SUPPORTS_NUMA_BALANCING if NUMA
-	select ARCH_SUPPORTS_PER_VMA_LOCK
 	select ARCH_SUPPORTS_RT
 	select ARCH_SUPPORTS_SCHED_SMT if SMP
 	select ARCH_SUPPORTS_SCHED_MC  if SMP

diff --git a/arch/powerpc/platforms/powernv/Kconfig b/arch/powerpc/platforms/powernv/Kconfig
index b5ad7c173ef0..dd8f6060fb7a 100644
--- a/arch/powerpc/platforms/powernv/Kconfig
+++ b/arch/powerpc/platforms/powernv/Kconfig

@@ -17,7 +17,6 @@ config PPC_POWERNV
 	select PPC_DOORBELL
 	select MMU_NOTIFIER
 	select FORCE_SMP
-	select ARCH_SUPPORTS_PER_VMA_LOCK
 	select PPC_RADIX_BROADCAST_TLBIE if PPC_RADIX_MMU
 	default y

diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
index 74910ce3a541..7d125e288f6e 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig

@@ -23,7 +23,6 @@ config PPC_PSERIES
 	select HOTPLUG_CPU
 	select FORCE_SMP
 	select SWIOTLB
-	select ARCH_SUPPORTS_PER_VMA_LOCK
 	select PPC_RADIX_BROADCAST_TLBIE if PPC_RADIX_MMU
 	default y

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 7b9c373d82fa..faa85a031fe5 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig

@@ -70,7 +70,6 @@ config RISCV
 	select ARCH_SUPPORTS_LTO_CLANG_THIN
 	select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS if 64BIT && MMU
 	select ARCH_SUPPORTS_PAGE_TABLE_CHECK if MMU
-	select ARCH_SUPPORTS_PER_VMA_LOCK if MMU
 	select ARCH_HAS_PTE_PROTNONE if MMU
 	select ARCH_SUPPORTS_RT
 	select ARCH_SUPPORTS_SHADOW_CALL_STACK if HAVE_SHADOW_CALL_STACK

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index ab8fccc2cc4e..d1274bca8c39 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig

@@ -151,7 +151,6 @@ config S390
 	select ARCH_HAS_PTE_PROTNONE
 	select ARCH_SUPPORTS_NUMA_BALANCING
 	select ARCH_SUPPORTS_PAGE_TABLE_CHECK
-	select ARCH_SUPPORTS_PER_VMA_LOCK
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF
 	select ARCH_USE_SYM_ANNOTATIONS

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index fb298e219179..79479d29576f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig

@@ -27,7 +27,6 @@ config X86_64
 	select ARCH_HAS_GIGANTIC_PAGE
 	select ARCH_SUPPORTS_MSEAL_SYSTEM_MAPPINGS
 	select ARCH_SUPPORTS_INT128 if CC_HAS_INT128
-	select ARCH_SUPPORTS_PER_VMA_LOCK
 	select ARCH_SUPPORTS_HUGE_PFNMAP if TRANSPARENT_HUGEPAGE
 	select HAVE_ARCH_SOFT_DIRTY
 	select MODULES_USE_ELF_RELA

@@ -1846,7 +1845,6 @@ config X86_USER_SHADOW_STACK
 	bool "X86 userspace shadow stack"
 	depends on AS_WRUSS
 	depends on X86_64
-	depends on PER_VMA_LOCK
 	select ARCH_USES_HIGH_VMA_FLAGS
 	select ARCH_HAS_USER_SHADOW_STACK
 	select X86_CET

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index b232e1098117..6713757da099 100644
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h

@@ -385,10 +385,8 @@ struct mem_size_stats;
 
 struct proc_maps_locking_ctx {
 	struct mm_struct *mm;
-#ifdef CONFIG_PER_VMA_LOCK
 	bool mmap_locked;
 	struct vm_area_struct *locked_vma;
-#endif
 };
 
 struct proc_maps_private {

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 5c54aebe2118..e671b4fd8ded 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c

@@ -130,8 +130,6 @@ static void release_task_mempolicy(struct proc_maps_private *priv)
 }
 #endif
 
-#ifdef CONFIG_PER_VMA_LOCK
-
 static inline int lock_ctx_mm(struct proc_maps_locking_ctx *lock_ctx)
 {
 	int ret = mmap_read_lock_killable(lock_ctx->mm);

@@ -233,46 +231,6 @@ static inline void reacquire_rcu(struct proc_maps_private *priv)
 	vma_iter_set(&priv->iter, priv->lock_ctx.locked_vma->vm_end);
 }
 
-#else /* CONFIG_PER_VMA_LOCK */
-
-static inline int lock_ctx_mm(struct proc_maps_locking_ctx *lock_ctx)
-{
-	return mmap_read_lock_killable(lock_ctx->mm);
-}
-
-static inline void unlock_ctx_mm(struct proc_maps_locking_ctx *lock_ctx)
-{
-	mmap_read_unlock(lock_ctx->mm);
-}
-
-static inline bool lock_vma_range(struct seq_file *m,
-				  struct proc_maps_locking_ctx *lock_ctx)
-{
-	return lock_ctx_mm(lock_ctx) == 0;
-}
-
-static inline void unlock_vma_range(struct proc_maps_locking_ctx *lock_ctx)
-{
-	unlock_ctx_mm(lock_ctx);
-}
-
-static struct vm_area_struct *get_next_vma(struct proc_maps_private *priv,
-					   loff_t last_pos)
-{
-	return vma_next(&priv->iter);
-}
-
-static inline bool fallback_to_mmap_lock(struct proc_maps_private *priv,
-					 loff_t pos)
-{
-	return false;
-}
-
-static inline void drop_rcu(struct proc_maps_private *priv) {}
-static inline void reacquire_rcu(struct proc_maps_private *priv) {}
-
-#endif /* CONFIG_PER_VMA_LOCK */
-
 static struct vm_area_struct *proc_get_vma(struct seq_file *m, loff_t *ppos)
 {
 	struct proc_maps_private *priv = m->private;

@@ -560,8 +518,6 @@ static int pid_maps_open(struct inode *inode, struct file *file)
 		PROCMAP_QUERY_VMA_FLAGS				\
 )
 
-#ifdef CONFIG_PER_VMA_LOCK
-
 static int query_vma_setup(struct proc_maps_locking_ctx *lock_ctx)
 {
 	reset_lock_ctx(lock_ctx);

@@ -612,26 +568,6 @@ static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_locking_ct
 	return vma;
 }
 
-#else /* CONFIG_PER_VMA_LOCK */
-
-static int query_vma_setup(struct proc_maps_locking_ctx *lock_ctx)
-{
-	return mmap_read_lock_killable(lock_ctx->mm);
-}
-
-static void query_vma_teardown(struct proc_maps_locking_ctx *lock_ctx)
-{
-	mmap_read_unlock(lock_ctx->mm);
-}
-
-static struct vm_area_struct *query_vma_find_by_addr(struct proc_maps_locking_ctx *lock_ctx,
-						     unsigned long addr)
-{
-	return find_vma(lock_ctx->mm, addr);
-}
-
-#endif  /* CONFIG_PER_VMA_LOCK */
-
 static struct vm_area_struct *query_matching_vma(struct proc_maps_locking_ctx *lock_ctx,
 						 unsigned long addr, u32 flags)
 {

@@ -1314,8 +1250,6 @@ static const struct mm_walk_ops smaps_shmem_walk_ops = {
 	.walk_lock		= PGWALK_RDLOCK,
 };
 
-#ifdef CONFIG_PER_VMA_LOCK
-
 static const struct mm_walk_ops smaps_walk_vma_lock_ops = {
 	.pmd_entry		= smaps_pte_range,
 	.hugetlb_entry		= smaps_hugetlb_range,

@@ -1345,22 +1279,6 @@ get_smaps_shmem_walk_ops(struct proc_maps_private *priv)
 	return &smaps_shmem_walk_vma_lock_ops;
 }
 
-#else /* CONFIG_PER_VMA_LOCK */
-
-static inline const struct mm_walk_ops *
-get_smaps_walk_ops(struct proc_maps_private *priv)
-{
-	return &smaps_walk_ops;
-}
-
-static inline const struct mm_walk_ops *
-get_smaps_shmem_walk_ops(struct proc_maps_private *priv)
-{
-	return &smaps_shmem_walk_ops;
-}
-
-#endif /* CONFIG_PER_VMA_LOCK */
-
 /*
  * Gather mem stats from @vma with the indicated beginning
  * address @start, and keep them in @mss.

@@ -3497,7 +3415,6 @@ static const struct mm_walk_ops show_numa_ops = {
 	.walk_lock = PGWALK_RDLOCK,
 };
 
-#ifdef CONFIG_PER_VMA_LOCK
 static const struct mm_walk_ops show_numa_vma_lock_ops = {
 	.hugetlb_entry = gather_hugetlb_stats,
 	.pmd_entry = gather_pte_stats,

@@ -3512,16 +3429,6 @@ get_show_numa_ops(struct proc_maps_private *priv)
 	return &show_numa_vma_lock_ops;
 }
 
-#else /* CONFIG_PER_VMA_LOCK */
-
-static inline const struct mm_walk_ops *
-get_show_numa_ops(struct proc_maps_private *priv)
-{
-	return &show_numa_ops;
-}
-
-#endif /* CONFIG_PER_VMA_LOCK */
-
 /*
  * Display pages allocated per node and memory policy via /proc.
  */

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 13902368471e..d16a927fcada 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h

@@ -931,7 +931,6 @@ static inline void vma_numab_state_free(struct vm_area_struct *vma) {}
  * These must be here rather than mmap_lock.h as dependent on vm_fault type,
  * declared in this header.
  */
-#ifdef CONFIG_PER_VMA_LOCK
 static inline void release_fault_lock(struct vm_fault *vmf)
 {
 	if (vmf->flags & FAULT_FLAG_VMA_LOCK)

@@ -947,17 +946,6 @@ static inline void assert_fault_locked(const struct vm_fault *vmf)
 	else
 		mmap_assert_locked(vmf->vma->vm_mm);
 }
-#else
-static inline void release_fault_lock(struct vm_fault *vmf)
-{
-	mmap_read_unlock(vmf->vma->vm_mm);
-}
-
-static inline void assert_fault_locked(const struct vm_fault *vmf)
-{
-	mmap_assert_locked(vmf->vma->vm_mm);
-}
-#endif /* CONFIG_PER_VMA_LOCK */
 
 static inline bool mm_flags_test(int flag, const struct mm_struct *mm)
 {

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 6d815f6440c9..5413bd10fff2 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h

@@ -950,7 +950,6 @@ struct vm_area_struct {
 		vma_flags_t flags;
 	};
 
-#ifdef CONFIG_PER_VMA_LOCK
 	/*
 	 * Can only be written (using WRITE_ONCE()) while holding both:
 	 *  - mmap_lock (in write mode)

@@ -966,7 +965,7 @@ struct vm_area_struct {
 	 * slowpath.
 	 */
 	unsigned int vm_lock_seq;
-#endif
+
 	/*
 	 * Low 32-bits of anonymous page offset.
 	 * See vma_start_anon_pgoff() comment for details.

@@ -1003,7 +1002,6 @@ struct vm_area_struct {
 #ifdef CONFIG_NUMA_BALANCING
 	struct vma_numab_state *numab_state;	/* NUMA Balancing state */
 #endif
-#ifdef CONFIG_PER_VMA_LOCK
 	/*
 	 * Used to keep track of firstly, whether the VMA is attached, secondly,
 	 * if attached, how many read locks are taken, and thirdly, if the

@@ -1046,7 +1044,6 @@ struct vm_area_struct {
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 	struct lockdep_map vmlock_dep_map;
 #endif
-#endif
 #ifdef CONFIG_64BIT
 	/*
 	 * High 32-bits of anonymous page offset.

@@ -1254,7 +1251,6 @@ struct mm_struct {
 					  * init_mm.mmlist, and are protected
 					  * by mmlist_lock
 					  */
-#ifdef CONFIG_PER_VMA_LOCK
 		struct rcuwait vma_writer_wait;
 		/*
 		 * This field has lock-like semantics, meaning it is sometimes

@@ -1274,7 +1270,7 @@ struct mm_struct {
 		 * mmap_lock.
 		 */
 		seqcount_t mm_lock_seq;
-#endif
+
 		struct futex_mm_data	futex;
 
 		unsigned long hiwater_rss; /* High-watermark of RSS usage */

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index 87f77e3da77f..db2dbf84943c 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h

@@ -76,8 +76,6 @@ static inline void mmap_assert_write_locked(const struct mm_struct *mm)
 	rwsem_assert_held_write(&mm->mmap_lock);
 }
 
-#ifdef CONFIG_PER_VMA_LOCK
-
 #ifdef CONFIG_LOCKDEP
 #define __vma_lockdep_map(vma) (&vma->vmlock_dep_map)
 #else

@@ -297,6 +295,9 @@ int __vma_start_write(struct vm_area_struct *vma, int state);
  */
 static inline void vma_start_write(struct vm_area_struct *vma)
 {
+	if (!IS_ENABLED(CONFIG_MMU))
+		return;
+
 	if (__is_vma_write_locked(vma))
 		return;

@@ -319,6 +320,9 @@ static inline void vma_start_write(struct vm_area_struct *vma)
 static inline __must_check
 int vma_start_write_killable(struct vm_area_struct *vma)
 {
+	if (!IS_ENABLED(CONFIG_MMU))
+		return 0;
+
 	if (__is_vma_write_locked(vma))
 		return 0;

@@ -331,6 +335,11 @@ int vma_start_write_killable(struct vm_area_struct *vma)
  */
 static inline void vma_assert_write_locked(struct vm_area_struct *vma)
 {
+	if (!IS_ENABLED(CONFIG_MMU)) {
+		mmap_assert_write_locked(vma->vm_mm);
+		return;
+	}
+
 	VM_WARN_ON_ONCE_VMA(!__is_vma_write_locked(vma), vma);
 }

@@ -343,6 +352,11 @@ static inline void vma_assert_locked(struct vm_area_struct *vma)
 {
 	unsigned int refcnt;
 
+	if (!IS_ENABLED(CONFIG_MMU)) {
+		mmap_assert_locked(vma->vm_mm);
+		return;
+	}
+
 	if (IS_ENABLED(CONFIG_LOCKDEP)) {
 		if (!lock_is_held(__vma_lockdep_map(vma)))
 			vma_assert_write_locked(vma);

@@ -432,6 +446,9 @@ static inline bool vma_is_attached(struct vm_area_struct *vma)
  */
 static inline void vma_assert_attached(struct vm_area_struct *vma)
 {
+	if (!IS_ENABLED(CONFIG_MMU))
+		return;
+
 	WARN_ON_ONCE(!vma_is_attached(vma));
 }

@@ -442,6 +459,9 @@ static inline void vma_assert_detached(struct vm_area_struct *vma)
 
 static inline void vma_mark_attached(struct vm_area_struct *vma)
 {
+	if (!IS_ENABLED(CONFIG_MMU))
+		return;
+
 	vma_assert_write_locked(vma);
 	vma_assert_detached(vma);
 	refcount_set_release(&vma->vm_refcnt, 1);

@@ -451,6 +471,9 @@ void __vma_exclude_readers_for_detach(struct vm_area_struct *vma);
 
 static inline void vma_mark_detached(struct vm_area_struct *vma)
 {
+	if (!IS_ENABLED(CONFIG_MMU))
+		return;
+
 	vma_assert_write_locked(vma);
 	vma_assert_attached(vma);

@@ -484,54 +507,6 @@ struct vm_area_struct *lock_next_vma(struct mm_struct *mm,
 				     struct vma_iterator *iter,
 				     unsigned long address);
 
-#else /* CONFIG_PER_VMA_LOCK */
-
-static inline void mm_lock_seqcount_init(struct mm_struct *mm) {}
-static inline void mm_lock_seqcount_begin(struct mm_struct *mm) {}
-static inline void mm_lock_seqcount_end(struct mm_struct *mm) {}
-
-static inline bool mmap_lock_speculate_try_begin(struct mm_struct *mm, unsigned int *seq)
-{
-	return false;
-}
-
-static inline bool mmap_lock_speculate_retry(struct mm_struct *mm, unsigned int seq)
-{
-	return true;
-}
-static inline void vma_lock_init(struct vm_area_struct *vma, bool reset_refcnt) {}
-static inline void vma_end_read(struct vm_area_struct *vma) {}
-static inline void vma_start_write(struct vm_area_struct *vma) {}
-static inline __must_check
-int vma_start_write_killable(struct vm_area_struct *vma) { return 0; }
-static inline void vma_assert_write_locked(struct vm_area_struct *vma)
-		{ mmap_assert_write_locked(vma->vm_mm); }
-static inline bool vma_is_attached(struct vm_area_struct *vma)
-		{ return true; }
-static inline void vma_assert_attached(struct vm_area_struct *vma) {}
-static inline void vma_assert_detached(struct vm_area_struct *vma) {}
-static inline void vma_mark_attached(struct vm_area_struct *vma) {}
-static inline void vma_mark_detached(struct vm_area_struct *vma) {}
-
-static inline struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
-		unsigned long address)
-{
-	return NULL;
-}
-
-static inline void vma_assert_locked(struct vm_area_struct *vma)
-{
-	mmap_assert_locked(vma->vm_mm);
-}
-
-static inline void vma_assert_stabilised(struct vm_area_struct *vma)
-{
-	/* If no VMA locks, then either mmap lock suffices to stabilise. */
-	mmap_assert_locked(vma->vm_mm);
-}
-
-#endif /* CONFIG_PER_VMA_LOCK */
-
 static inline void vma_assert_can_modify(struct vm_area_struct *vma)
 {
 	if (vma_is_attached(vma))

diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
index 41fe87d7302f..6bd6022b6b84 100644
--- a/kernel/bpf/stackmap.c
+++ b/kernel/bpf/stackmap.c

@@ -272,13 +272,10 @@ struct stack_map_vma_lock {
 /*
  * Acquire a stable read-side reference on the VMA covering @ip.
  *
- * With CONFIG_PER_VMA_LOCK=y this returns a VMA with its per-VMA read
- * lock held and mmap_lock dropped, so the caller may sleep.
- *
- * With CONFIG_PER_VMA_LOCK=n it returns a VMA with mmap_lock still
- * held; the caller must snapshot any fields it needs and pin vm_file
- * with get_file() before stack_map_unlock_vma() drops mmap_lock, as
- * the VMA may be split, merged, or freed after that.
+ * On NOMMU configurations, returns with the mmap_lock held.  If the MMU
+ * is enabled, the per-VMA lock will be held instead.  The lock
+ * should be released with stack_map_unlock_vma() which will release the
+ * appropriate lock.  Once the lock is released, the VMA may be freed.
  *
  * Returns NULL on failure, in which case no lock is held.
  */

@@ -288,7 +285,6 @@ stack_map_lock_vma(struct stack_map_vma_lock *lock, unsigned long ip)
 	struct mm_struct *mm = lock->mm;
 	struct vm_area_struct *vma;
 
-	/* noop under !CONFIG_PER_VMA_LOCK */
 	vma = lock_vma_under_rcu(mm, ip);
 	if (vma) {
 		lock->vma = vma;

@@ -308,21 +304,20 @@ stack_map_lock_vma(struct stack_map_vma_lock *lock, unsigned long ip)
 		return NULL;
 	}
 
-#ifdef CONFIG_PER_VMA_LOCK
+#ifdef CONFIG_MMU
 	if (!vma_start_read_locked(vma)) {
 		mmap_read_unlock(mm);
 		return NULL;
 	}
 	mmap_read_unlock(mm);
 #endif
-
 	lock->vma = vma;
 	return vma;
 }
 
 static void stack_map_unlock_vma(struct stack_map_vma_lock *lock)
 {
-#ifdef CONFIG_PER_VMA_LOCK
+#ifdef CONFIG_MMU
 	vma_end_read(lock->vma);
 #else
 	mmap_read_unlock(lock->mm);

diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
index e791ae065c39..245f74ec491d 100644
--- a/kernel/bpf/task_iter.c
+++ b/kernel/bpf/task_iter.c

@@ -835,7 +835,7 @@ __bpf_kfunc int bpf_iter_task_vma_new(struct bpf_iter_task_vma *it,
 	BUILD_BUG_ON(sizeof(struct bpf_iter_task_vma_kern) != sizeof(struct bpf_iter_task_vma));
 	BUILD_BUG_ON(__alignof__(struct bpf_iter_task_vma_kern) != __alignof__(struct bpf_iter_task_vma));
 
-	if (!IS_ENABLED(CONFIG_PER_VMA_LOCK)) {
+	if (!IS_ENABLED(CONFIG_MMU)) {
 		kit->data = NULL;
 		return -EOPNOTSUPP;
 	}

diff --git a/kernel/fork.c b/kernel/fork.c
index f0e2e131a9a5..ff91f5f66c80 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c

@@ -1077,9 +1077,7 @@ static void mmap_init_lock(struct mm_struct *mm)
 {
 	init_rwsem(&mm->mmap_lock);
 	mm_lock_seqcount_init(mm);
-#ifdef CONFIG_PER_VMA_LOCK
 	rcuwait_init(&mm->vma_writer_wait);
-#endif
 }
 
 static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p)

diff --git a/mm/Kconfig b/mm/Kconfig
index 8a24c130d008..bf89d7d3be4b 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig

@@ -1429,18 +1429,6 @@ config LRU_GEN_WALKS_MMU
 	depends on LRU_GEN && ARCH_HAS_HW_PTE_YOUNG
 # }
 
-config ARCH_SUPPORTS_PER_VMA_LOCK
-       def_bool n
-
-config PER_VMA_LOCK
-	def_bool y
-	depends on ARCH_SUPPORTS_PER_VMA_LOCK && MMU && SMP
-	help
-	  Allow per-vma locking during page fault handling.
-
-	  This feature allows locking each virtual memory area separately when
-	  handling page faults instead of taking mmap_lock.
-
 config LOCK_MM_AND_FIND_VMA
 	bool
 	depends on !STACK_GROWSUP

diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 5737a504efbb..1dd150edfe71 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug

@@ -310,7 +310,6 @@ config DEBUG_KMEMLEAK_VERBOSE
 
 config PER_VMA_LOCK_STATS
 	bool "Statistics for per-vma locks"
-	depends on PER_VMA_LOCK
 	help
 	  Say Y here to enable success, retry and failure counters of page
 	  faults handled under protection of per-vma locks. When enabled, the

diff --git a/mm/debug.c b/mm/debug.c
index 9a0297b3988d..655e6bcc0e8d 100644
--- a/mm/debug.c
+++ b/mm/debug.c

@@ -157,17 +157,13 @@ void dump_vma(const struct vm_area_struct *vma)
 	pr_emerg("vma %px start %px end %px mm %px\n"
 		"prot %lx anon_vma %px vm_ops %px\n"
 		"pgoff %lx file %px private_data %px\n"
-#ifdef CONFIG_PER_VMA_LOCK
 		"refcnt %x\n"
-#endif
 		"flags: %#lx(%pGv)\n",
 		vma, (void *)vma->vm_start, (void *)vma->vm_end, vma->vm_mm,
 		(unsigned long)pgprot_val(vma->vm_page_prot),
 		vma->anon_vma, vma->vm_ops, vma_start_pgoff(vma),
 		vma->vm_file, vma->vm_private_data,
-#ifdef CONFIG_PER_VMA_LOCK
 		refcount_read(&vma->vm_refcnt),
-#endif
 		vma->vm_flags, &vma->vm_flags);
 }
 EXPORT_SYMBOL(dump_vma);

diff --git a/mm/init-mm.c b/mm/init-mm.c
index 3e792aad7626..a1bb2c2d0284 100644
--- a/mm/init-mm.c
+++ b/mm/init-mm.c

@@ -39,10 +39,8 @@ struct mm_struct init_mm = {
 	.page_table_lock =  __SPIN_LOCK_UNLOCKED(init_mm.page_table_lock),
 	.arg_lock	=  __SPIN_LOCK_UNLOCKED(init_mm.arg_lock),
 	.mmlist		= LIST_HEAD_INIT(init_mm.mmlist),
-#ifdef CONFIG_PER_VMA_LOCK
 	.vma_writer_wait = __RCUWAIT_INITIALIZER(init_mm.vma_writer_wait),
 	.mm_lock_seq	= SEQCNT_ZERO(init_mm.mm_lock_seq),
-#endif
 #ifdef CONFIG_SCHED_MM_CID
 	.mm_cid.lock = __RAW_SPIN_LOCK_UNLOCKED(init_mm.mm_cid.lock),
 #endif

diff --git a/mm/memory.c b/mm/memory.c
index 4134ac607ee0..21a4d95cb409 100644
--- a/mm/memory.c
+++ b/mm/memory.c

@@ -6818,7 +6818,6 @@ static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma,
 				 !vma_is_cow_mapping(vma)))
 			return VM_FAULT_SIGSEGV;
 	}
-#ifdef CONFIG_PER_VMA_LOCK
 	/*
 	 * Per-VMA locks can't be used with FAULT_FLAG_RETRY_NOWAIT because of
 	 * the assumption that lock is dropped on VM_FAULT_RETRY.

@@ -6827,7 +6826,6 @@ static vm_fault_t sanitize_fault_flags(struct vm_area_struct *vma,
 			(FAULT_FLAG_VMA_LOCK | FAULT_FLAG_RETRY_NOWAIT)) ==
 			(FAULT_FLAG_VMA_LOCK | FAULT_FLAG_RETRY_NOWAIT)))
 		return VM_FAULT_SIGSEGV;
-#endif
 
 	return 0;
 }

diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c
index 898c2ef1e958..272f9ac762b9 100644
--- a/mm/mmap_lock.c
+++ b/mm/mmap_lock.c

@@ -43,9 +43,6 @@ void __mmap_lock_do_trace_released(struct mm_struct *mm, bool write)
 EXPORT_SYMBOL(__mmap_lock_do_trace_released);
 #endif /* CONFIG_TRACING */
 
-#ifdef CONFIG_MMU
-#ifdef CONFIG_PER_VMA_LOCK
-
 /* State shared across __vma_[start, end]_exclude_readers. */
 struct vma_exclude_readers_state {
 	/* Input parameters. */

@@ -299,6 +296,8 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 	MA_STATE(mas, &mm->mm_mt, address, address);
 	struct vm_area_struct *vma;
 
+	if (!IS_ENABLED(CONFIG_MMU))
+		return NULL;
 retry:
 	rcu_read_lock();
 	vma = mas_walk(&mas);

@@ -431,7 +430,6 @@ struct vm_area_struct *lock_next_vma(struct mm_struct *mm,
 
 	return vma;
 }
-#endif /* CONFIG_PER_VMA_LOCK */
 
 #ifdef CONFIG_LOCK_MM_AND_FIND_VMA
 #include <linux/extable.h>

@@ -548,23 +546,3 @@ struct vm_area_struct *lock_mm_and_find_vma(struct mm_struct *mm,
 	return NULL;
 }
 #endif /* CONFIG_LOCK_MM_AND_FIND_VMA */
-
-#else /* CONFIG_MMU */
-
-/*
- * At least xtensa ends up having protection faults even with no
- * MMU.. No stack expansion, at least.
- */
-struct vm_area_struct *lock_mm_and_find_vma(struct mm_struct *mm,
-			unsigned long addr, struct pt_regs *regs)
-{
-	struct vm_area_struct *vma;
-
-	mmap_read_lock(mm);
-	vma = vma_lookup(mm, addr);
-	if (!vma)
-		mmap_read_unlock(mm);
-	return vma;
-}
-
-#endif /* CONFIG_MMU */

diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index ed4860c01936..fbcf64c59a97 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c

@@ -446,7 +446,6 @@ static inline void process_mm_walk_lock(struct mm_struct *mm,
 static inline void process_vma_walk_lock(struct vm_area_struct *vma,
 					 enum page_walk_lock walk_lock)
 {
-#ifdef CONFIG_PER_VMA_LOCK
 	switch (walk_lock) {
 	case PGWALK_WRLOCK:
 		vma_start_write(vma);

@@ -461,7 +460,6 @@ static inline void process_vma_walk_lock(struct vm_area_struct *vma,
 		/* PGWALK_RDLOCK is handled by process_mm_walk_lock */
 		break;
 	}
-#endif
 }
 
 /*

diff --git a/mm/rmap.c b/mm/rmap.c
index 14f2f9b07572..7515220dfea4 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c

@@ -260,11 +260,9 @@ static void check_anon_vma_clone(struct vm_area_struct *dst,
 	/* For the anon_vma to be compatible, it can only be singular. */
 	VM_WARN_ON_ONCE(operation == VMA_OP_MERGE_UNFAULTED &&
 			!list_is_singular(&src->anon_vma_chain));
-#ifdef CONFIG_PER_VMA_LOCK
 	/* Only merging an unfaulted VMA leaves the destination attached. */
 	VM_WARN_ON_ONCE(operation != VMA_OP_MERGE_UNFAULTED &&
 			vma_is_attached(dst));
-#endif
 }
 
 static void maybe_reuse_anon_vma(struct vm_area_struct *dst,

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 23fb68fce000..0b279b82eaa6 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c

@@ -122,7 +122,6 @@ struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm,
 	return vma;
 }
 
-#ifdef CONFIG_PER_VMA_LOCK
 /*
  * uffd_lock_vma() - Lookup and lock vma corresponding to @address.
  * @mm: mm to search vma in.

@@ -182,34 +181,6 @@ static void uffd_mfill_unlock(struct vm_area_struct *vma)
 	vma_end_read(vma);
 }
 
-#else
-
-static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
-					      unsigned long dst_start,
-					      unsigned long len)
-{
-	struct vm_area_struct *dst_vma;
-
-	mmap_read_lock(dst_mm);
-	dst_vma = find_vma_and_prepare_anon(dst_mm, dst_start);
-	if (IS_ERR(dst_vma))
-		goto out_unlock;
-
-	if (validate_dst_vma(dst_vma, dst_start + len))
-		return dst_vma;
-
-	dst_vma = ERR_PTR(-ENOENT);
-out_unlock:
-	mmap_read_unlock(dst_mm);
-	return dst_vma;
-}
-
-static void uffd_mfill_unlock(struct vm_area_struct *vma)
-{
-	mmap_read_unlock(vma->vm_mm);
-}
-#endif
-
 static void mfill_put_vma(struct mfill_state *state)
 {
 	if (!state->vma)

@@ -1850,7 +1821,6 @@ int find_vmas_mm_locked(struct mm_struct *mm,
 	return 0;
 }
 
-#ifdef CONFIG_PER_VMA_LOCK
 static int uffd_move_lock(struct mm_struct *mm,
 			  unsigned long dst_start,
 			  unsigned long src_start,

@@ -1925,31 +1895,6 @@ static void uffd_move_unlock(struct vm_area_struct *dst_vma,
 		vma_end_read(dst_vma);
 }
 
-#else
-
-static int uffd_move_lock(struct mm_struct *mm,
-			  unsigned long dst_start,
-			  unsigned long src_start,
-			  struct vm_area_struct **dst_vmap,
-			  struct vm_area_struct **src_vmap)
-{
-	int err;
-
-	mmap_read_lock(mm);
-	err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
-	if (err)
-		mmap_read_unlock(mm);
-	return err;
-}
-
-static void uffd_move_unlock(struct vm_area_struct *dst_vma,
-			     struct vm_area_struct *src_vma)
-{
-	mmap_assert_locked(src_vma->vm_mm);
-	mmap_read_unlock(dst_vma->vm_mm);
-}
-#endif
-
 /**
  * move_pages - move arbitrary anonymous pages of an existing vma
  * @ctx: pointer to the userfaultfd context

diff --git a/rust/kernel/mm.rs b/rust/kernel/mm.rs
index 4764d7b68f2a..f4fa54616085 100644
--- a/rust/kernel/mm.rs
+++ b/rust/kernel/mm.rs

@@ -170,30 +170,20 @@ pub unsafe fn from_raw<'a>(ptr: *const bindings::mm_struct) -> &'a MmWithUser {
     ///
     /// This is an optimistic trylock operation, so it may fail if there is contention. In that
     /// case, you should fall back to taking the mmap read lock.
-    ///
-    /// When per-vma locks are disabled, this always returns `None`.
     #[inline]
     pub fn lock_vma_under_rcu(&self, vma_addr: usize) -> Option<VmaReadGuard<'_>> {
-        #[cfg(CONFIG_PER_VMA_LOCK)]
-        {
-            // SAFETY: Calling `bindings::lock_vma_under_rcu` is always okay given an mm where
-            // `mm_users` is non-zero.
-            let vma = unsafe { bindings::lock_vma_under_rcu(self.as_raw(), vma_addr) };
-            if !vma.is_null() {
-                return Some(VmaReadGuard {
-                    // SAFETY: If `lock_vma_under_rcu` returns a non-null ptr, then it points at a
-                    // valid vma. The vma is stable for as long as the vma read lock is held.
-                    vma: unsafe { VmaRef::from_raw(vma) },
-                    _nts: NotThreadSafe,
-                });
-            }
+        // SAFETY: Calling `bindings::lock_vma_under_rcu` is always okay given an mm where
+        // `mm_users` is non-zero.
+        let vma = unsafe { bindings::lock_vma_under_rcu(self.as_raw(), vma_addr) };
+        if vma.is_null() {
+            return None;
         }
-
-        // Silence warnings about unused variables.
-        #[cfg(not(CONFIG_PER_VMA_LOCK))]
-        let _ = vma_addr;
-
-        None
+        Some(VmaReadGuard {
+            // SAFETY: If `lock_vma_under_rcu` returns a non-null ptr, then it points at a
+            // valid vma. The vma is stable for as long as the vma read lock is held.
+            vma: unsafe { VmaRef::from_raw(vma) },
+            _nts: NotThreadSafe,
+        })
     }
 
     /// Lock the mmap read lock.

diff --git a/tools/testing/vma/include/dup.h b/tools/testing/vma/include/dup.h
index 41203b1c2323..a0d1d563da24 100644
--- a/tools/testing/vma/include/dup.h
+++ b/tools/testing/vma/include/dup.h

@@ -582,7 +582,6 @@ struct vm_area_struct {
 		vma_flags_t flags;
 	};
 
-#ifdef CONFIG_PER_VMA_LOCK
 	/*
 	 * Can only be written (using WRITE_ONCE()) while holding both:
 	 *  - mmap_lock (in write mode)

@@ -598,7 +597,7 @@ struct vm_area_struct {
 	 * slowpath.
 	 */
 	unsigned int vm_lock_seq;
-#endif
+
 	unsigned int __vm_anon_pgoff_lo;
 
 	/*

@@ -632,10 +631,8 @@ struct vm_area_struct {
 #ifdef CONFIG_NUMA_BALANCING
 	struct vma_numab_state *numab_state;	/* NUMA Balancing state */
 #endif
-#ifdef CONFIG_PER_VMA_LOCK
 	/* Unstable RCU readers are allowed to read this. */
 	refcount_t vm_refcnt;
-#endif
 #ifdef CONFIG_64BIT
 	unsigned int __vm_anon_pgoff_hi;
 #endif

diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h
index 8a48b231aa7a..54d5c3360aa2 100644
--- a/tools/testing/vma/vma_internal.h
+++ b/tools/testing/vma/vma_internal.h

@@ -15,7 +15,6 @@
 #include <stdlib.h>
 
 #define CONFIG_MMU		1
-#define CONFIG_PER_VMA_LOCK	1
 
 #ifdef __CONCAT
 #undef __CONCAT

-- 
2.55.0.691.gc56d675ccc-goog

[PATCH v5 2/5] binder: Make shrinker rely solely on per-VMA lock

From: Suren Baghdasaryan <surenb@google.com>
Date: 2026-08-12 01:11:14

From: Dave Hansen <dave.hansen@linux.intel.com>

tl;dr: lock_vma_under_rcu() is already a trylock. No need to do both
it and mmap_read_trylock().

Long Version:

== Background ==

Historically, binder used an mmap_read_trylock() in its shrinker code.
This ensures that reclaim is not blocked on an mmap_lock. Commit
95bc2d4a9020 ("binder: use per-vma lock in page reclaiming") added
support for the per-VMA lock, but left mmap_read_trylock() as a
fallback.

This was presumably because the per-VMA locking can fail for several
reasons and most (all?) lock_vma_under_rcu() callers have a fallback
to mmap_read_trylock().

== Problem ==

The fallback is not worth the complexity here. lock_vma_under_rcu() is
essentially already a non-blocking trylock. The main reason it fails
is also the reason mmap_read_trylock() fails: something is holding
mmap_write_lock().

The only remedy for a collision with mmap_write_lock() is to wait,
which this code can not do. So the "fallback" after
lock_vma_under_rcu() failure is not really a fallback: it is really
likely to just be retrying in vain. That retry in an of itself isn't
horrible. But it adds complexity.

== Solution ==

Now that per-VMA locks are universally available, lock_vma_under_rcu()
will not persistently fail. Rely on it alone and simplify the code.
The removal of the fallback does not affect NOMMU case because binder
driver depends on CONFIG_MMU.

While at it we also make the handling of the cases where the original
binder VMA is gone consistent. There are two cases to consider when
Binder VMA is gone:
1. there is no VMA at that location anymore.
2. there is now another unrelated VMA at that location.

Before this change we handle case 1 by having the shrinker proceed to
free the page, and just skip the zap_vma_range() call. And we handle
case 2 by having the shrinker return LRU_SKIP. While either behavior
is acceptable, we need to handle them in a consistent way. Handle both
cases by freeing the page without touching the VMA (skipping the
zap_vma_range()).

Full disclosure: I originally tried to do this with
lock_vma_under_rcu_wait(), but it did not fit well with the mmap_lock
trylock semantics. Claude caught this in a review and suggested the
approach in this path. It seemed sane to me. So, Suggesed-by: Claude,
I guess.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Liam R. Howlett <redacted>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: linux-mm@kvack.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Todd Kjos <tkjos@android.com>
Cc: Christian Brauner <christian@brauner.io>
Cc: Carlos Llamas <cmllamas@google.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Ahern <dsahern@kernel.org>
Cc: netdev@vger.kernel.org
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 drivers/android/binder_alloc.c | 45 ++++++++++++++++------------------
 1 file changed, 21 insertions(+), 24 deletions(-)

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index e4488ad86a65..c13a588c37de 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c

@@ -1142,7 +1142,6 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
 	struct vm_area_struct *vma;
 	struct page *page_to_free;
 	unsigned long page_addr;
-	int mm_locked = 0;
 	size_t index;
 
 	if (!mmget_not_zero(mm))

@@ -1151,27 +1150,25 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
 	index = mdata->page_index;
 	page_addr = alloc->vm_start + index * PAGE_SIZE;
 
-	/* attempt per-vma lock first */
+	/*
+	 * Attempt per-vma lock. This is essentially a
+	 * "trylock". It can fail even if the VMA exists
+	 * for 'page_addr'.
+	 */
 	vma = lock_vma_under_rcu(mm, page_addr);
 	if (!vma) {
-		/* fall back to mmap_lock */
-		if (!mmap_read_trylock(mm))
-			goto err_mmap_read_lock_failed;
-		mm_locked = 1;
-		vma = vma_lookup(mm, page_addr);
+		/*
+		 * If the vma exists, we can't continue because we cannot
+		 * remove the page from the vma. However, if the vma was
+		 * unmapped, it's okay to continue.
+		 */
+		if (binder_alloc_is_mapped(alloc))
+			goto err_vma_lock_failed;
 	}
 
 	if (!mutex_trylock(&alloc->mutex))
 		goto err_get_alloc_mutex_failed;
 
-	/*
-	 * Since a binder_alloc can only be mapped once, we ensure
-	 * the vma corresponds to this mapping by checking whether
-	 * the binder_alloc is still mapped.
-	 */
-	if (vma && !binder_alloc_is_mapped(alloc))
-		goto err_invalid_vma;
-
 	trace_binder_unmap_kernel_start(alloc, index);
 
 	page_to_free = alloc->pages[index];

@@ -1182,7 +1179,12 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
 	list_lru_isolate(lru, item);
 	spin_unlock(&lru->lock);
 
-	if (vma) {
+	/*
+	 * Since a binder_alloc can only be mapped once, we ensure
+	 * the vma corresponds to this mapping by checking whether
+	 * the binder_alloc is still mapped.
+	 */
+	if (vma && binder_alloc_is_mapped(alloc)) {
 		trace_binder_unmap_user_start(alloc, index);
 
 		zap_vma_range(vma, page_addr, PAGE_SIZE);

@@ -1191,23 +1193,18 @@ enum lru_status binder_alloc_free_page(struct list_head *item,
 	}
 
 	mutex_unlock(&alloc->mutex);
-	if (mm_locked)
-		mmap_read_unlock(mm);
-	else
+	if (vma)
 		vma_end_read(vma);
 	mmput_async(mm);
 	binder_free_page(page_to_free);
 
 	return LRU_REMOVED_RETRY;
 
-err_invalid_vma:
 	mutex_unlock(&alloc->mutex);
 err_get_alloc_mutex_failed:
-	if (mm_locked)
-		mmap_read_unlock(mm);
-	else
+	if (vma)
 		vma_end_read(vma);
-err_mmap_read_lock_failed:
+err_vma_lock_failed:
 	mmput_async(mm);
 err_mmget:
 	return LRU_SKIP;

-- 
2.55.0.691.gc56d675ccc-goog

[PATCH v5 3/5] mm: Add RCU-based VMA lookup helper that waits for writers

From: Suren Baghdasaryan <surenb@google.com>
Date: 2026-08-12 01:11:19

From: Dave Hansen <dave.hansen@linux.intel.com>

There are basically two parallel ways to look up a VMA: the traditional
way, which is protected by mmap_read_lock, and the RCU-based per-VMA
lock way which is based on RCU and refcounts. However, per-VMA locks
will fail if the lock is help by a writer and therefore never waits.
In a number of places we need to wait for the lock and it's done by
falling back to mmap_read_lock, locking the VMA and releasing the
mmap_lock once VMA is locked.

Add vma_start_read_unlocked() - a variant of the RCU-based lookup that
waits for writers. This is basically the same as the existing RCU-based
lookup, but on a failure to lock it temporarily takes mmap_lock for read
and waits for writers to finish before locking the VMA, dropping the
mmap_read_lock and returning the locked VMA. This has some advantages:

 1. Callers do not need to have a fallback path for when they
    collide with writers.
 2. Its fast path does not require taking mmap_lock for read.

Basically, when applied correctly, this approach results in faster
*and* simpler code.

While at it, fix the comments for vma_start_read_locked(),
vma_start_read_locked_nested(), and uffd_lock_vma().

Suggested-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Liam R. Howlett <redacted>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: linux-mm@kvack.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Todd Kjos <tkjos@android.com>
Cc: Christian Brauner <christian@brauner.io>
Cc: Carlos Llamas <cmllamas@google.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Ahern <dsahern@kernel.org>
Cc: netdev@vger.kernel.org
Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 include/linux/mmap_lock.h | 19 +++++++++++++++----
 mm/mmap_lock.c            | 35 +++++++++++++++++++++++++++++++++++
 mm/userfaultfd.c          |  6 ++++--
 3 files changed, 54 insertions(+), 6 deletions(-)

diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
index db2dbf84943c..5a3626dd0c18 100644
--- a/include/linux/mmap_lock.h
+++ b/include/linux/mmap_lock.h

@@ -228,10 +228,14 @@ static inline void vma_refcount_put(struct vm_area_struct *vma)
 }
 
 /*
- * Use only while holding mmap read lock which guarantees that locking will not
- * fail (nobody can concurrently write-lock the vma). vma_start_read() should
+ * Use only while holding mmap read lock which guarantees that vma lock is not
+ * contended (nobody can concurrently write-lock the vma). vma_start_read() should
  * not be used in such cases because it might fail due to mm_lock_seq overflow.
  * This functionality is used to obtain vma read lock and drop the mmap read lock.
+ *
+ * VMA can't be detached while we are holding mmap lock, therefore in practice this
+ * function can fail only when there are so many readers that vm_refcnt overflows.
+ * The failure case is very unlikely and is already annotated as such internally.
  */
 static inline bool vma_start_read_locked_nested(struct vm_area_struct *vma, int subclass)
 {

@@ -247,16 +251,23 @@ static inline bool vma_start_read_locked_nested(struct vm_area_struct *vma, int
 }
 
 /*
- * Use only while holding mmap read lock which guarantees that locking will not
- * fail (nobody can concurrently write-lock the vma). vma_start_read() should
+ * Use only while holding mmap read lock which guarantees that vma lock is not
+ * contended (nobody can concurrently write-lock the vma). vma_start_read() should
  * not be used in such cases because it might fail due to mm_lock_seq overflow.
  * This functionality is used to obtain vma read lock and drop the mmap read lock.
+ *
+ * VMA can't be detached while we are holding mmap lock, therefore in practice this
+ * function can fail only when there are so many readers that vm_refcnt overflows.
+ * The failure case is very unlikely and is already annotated as such internally.
  */
 static inline bool vma_start_read_locked(struct vm_area_struct *vma)
 {
 	return vma_start_read_locked_nested(vma, 0);
 }
 
+struct vm_area_struct *vma_start_read_unlocked(struct mm_struct *mm,
+					       unsigned long address);
+
 static inline void vma_end_read(struct vm_area_struct *vma)
 {
 	vma_refcount_put(vma);

diff --git a/mm/mmap_lock.c b/mm/mmap_lock.c
index 272f9ac762b9..2f94ee0fdee2 100644
--- a/mm/mmap_lock.c
+++ b/mm/mmap_lock.c

@@ -340,6 +340,41 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm,
 	return NULL;
 }
 
+/**
+ * vma_start_read_unlocked() - Find the VMA covering 'address' and read-lock it.
+ * @mm: the mm_struct of the address space to search
+ * @address: address that the vma should contain
+ *
+ * The fast path does not take mmap_lock. Waits for writers to finish if the
+ * VMA is being modified by taking mmap_lock.
+ * Use when mmap_lock is not held, otherwise use vma_start_read_locked().
+ * Nothing prevents VMAs being unmapped/mapped before or after the VMA is
+ * looked up, if a stronger guarantee is required, take an mmap_lock.
+ *
+ * Return: If a VMA exists which spans @address, return that VMA, read-locked.
+ * If no VMA is mapped there or, very unlikely, a reference count overflow
+ * occurred, return NULL.
+ */
+struct vm_area_struct *vma_start_read_unlocked(struct mm_struct *mm,
+					       unsigned long address)
+{
+	struct vm_area_struct *vma;
+
+	/* Fast path: return stable VMA covering 'address': */
+	vma = lock_vma_under_rcu(mm, address);
+	if (vma)
+		return vma;
+
+	/* Slow path: preclude VMA writers by temporarily getting mmap read lock. */
+	mmap_read_lock(mm);
+	vma = vma_lookup(mm, address);
+	if (vma && !vma_start_read_locked(vma))
+		vma = NULL;
+	mmap_read_unlock(mm);
+
+	return vma;
+}
+
 static struct vm_area_struct *lock_next_vma_under_mmap_lock(struct mm_struct *mm,
 							    struct vma_iterator *vmi,
 							    unsigned long from_addr)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 0b279b82eaa6..d17ca4d2bb39 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c

@@ -129,8 +129,10 @@ struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm,
  *
  * Should be called without holding mmap_lock.
  *
- * Return: A locked vma containing @address, -ENOENT if no vma is found, or
- * -ENOMEM if anon_vma couldn't be allocated.
+ * Return: A locked vma containing @address, -ENOENT if no vma is found,
+ * -ENOMEM if anon_vma couldn't be allocated, or -EAGAIN if vma refcount
+ * overflow happened due to high number of readers and the caller should
+ * retry later.
  */
 static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm,
 				       unsigned long address)

-- 
2.55.0.691.gc56d675ccc-goog

[PATCH v5 4/5] binder: Remove mmap_lock fallback

From: Suren Baghdasaryan <surenb@google.com>
Date: 2026-08-12 01:11:24

From: Dave Hansen <dave.hansen@linux.intel.com>

Previously, the per-VMA locking could fail in the face of writers
which necessitate a fallback to mmap_lock. The new
vma_start_read_unlocked() will wait for writers instead of failing.

Use the new helper. Wait for writers. Remove the fallback to mmap_lock.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Liam R. Howlett <redacted>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: linux-mm@kvack.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Todd Kjos <tkjos@android.com>
Cc: Christian Brauner <christian@brauner.io>
Cc: Carlos Llamas <cmllamas@google.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Ahern <dsahern@kernel.org>
Cc: netdev@vger.kernel.org
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 drivers/android/binder/page_range.rs | 19 +++----------------
 drivers/android/binder_alloc.c       | 17 +++++------------
 rust/kernel/mm.rs                    | 27 +++++++++++++++++++++++++++
 3 files changed, 35 insertions(+), 28 deletions(-)

diff --git a/drivers/android/binder/page_range.rs b/drivers/android/binder/page_range.rs
index e82a5523804f..f7ad88a0d806 100644
--- a/drivers/android/binder/page_range.rs
+++ b/drivers/android/binder/page_range.rs

@@ -439,22 +439,9 @@ unsafe fn use_page_slow(&self, i: usize) -> Result<()> {
         // workqueue.
         let mm = MmWithUser::into_mmput_async(self.mm.mmget_not_zero().ok_or(ESRCH)?);
         {
-            let vma_read;
-            let mmap_read;
-            let vma = if let Some(ret) = mm.lock_vma_under_rcu(vma_addr) {
-                vma_read = ret;
-                check_vma(&vma_read, self)
-            } else {
-                mmap_read = mm.mmap_read_lock();
-                mmap_read
-                    .vma_lookup(vma_addr)
-                    .and_then(|vma| check_vma(vma, self))
-            };
-
-            match vma {
-                Some(vma) => vma.vm_insert_page(user_page_addr, &new_page)?,
-                None => return Err(ESRCH),
-            }
+            let vma_read_guard = mm.vma_start_read_unlocked(vma_addr).ok_or(ESRCH)?;
+            let vma = check_vma(&vma_read_guard, self).ok_or(ESRCH)?;
+            vma.vm_insert_page(user_page_addr, &new_page)?;
         }
 
         let inner = self.lock.lock();

diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index c13a588c37de..efa23f6b8360 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c

@@ -259,21 +259,14 @@ static int binder_page_insert(struct binder_alloc *alloc,
 	struct vm_area_struct *vma;
 	int ret = -ESRCH;
 
-	/* attempt per-vma lock first */
-	vma = lock_vma_under_rcu(mm, addr);
-	if (vma) {
-		if (binder_alloc_is_mapped(alloc))
-			ret = vm_insert_page(vma, addr, page);
-		vma_end_read(vma);
+	vma = vma_start_read_unlocked(mm, addr);
+	if (!vma)
 		return ret;
-	}
 
-	/* fall back to mmap_lock */
-	mmap_read_lock(mm);
-	vma = vma_lookup(mm, addr);
-	if (vma && binder_alloc_is_mapped(alloc))
+	if (binder_alloc_is_mapped(alloc))
 		ret = vm_insert_page(vma, addr, page);
-	mmap_read_unlock(mm);
+
+	vma_end_read(vma);
 
 	return ret;
 }

diff --git a/rust/kernel/mm.rs b/rust/kernel/mm.rs
index f4fa54616085..11466fb304df 100644
--- a/rust/kernel/mm.rs
+++ b/rust/kernel/mm.rs

@@ -186,6 +186,33 @@ pub fn lock_vma_under_rcu(&self, vma_addr: usize) -> Option<VmaReadGuard<'_>> {
         })
     }
 
+    /// Find the VMA covering 'address' and read-lock it.
+    ///
+    /// The fast path does not take mmap_lock. Waits for writers to finish if the
+    /// VMA is being modified by taking mmap_lock.
+    /// Use when mmap_lock is not held, otherwise use vma_start_read_locked().
+    /// Nothing prevents VMAs being unmapped/mapped before or after the VMA is
+    /// looked up, if a stronger guarantee is required, take an mmap_lock.
+    ///
+    /// Return: If a VMA exists which spans @address, return that VMA, read-locked.
+    /// If no VMA is mapped there or, very unlikely, a reference count overflow
+    /// occurred, return NULL.
+    #[inline]
+    pub fn vma_start_read_unlocked(&self, vma_addr: usize) -> Option<VmaReadGuard<'_>> {
+        // SAFETY: We may invoke `vma_start_read_unlocked` because we know this `mm` has non-zero
+        // `mm_users`.
+        let vma = unsafe { bindings::vma_start_read_unlocked(self.as_raw(), vma_addr) };
+        if vma.is_null() {
+            return None;
+        }
+        Some(VmaReadGuard {
+            // SAFETY: If `vma_start_read_unlocked` returns a non-null ptr, then it points at a
+            // valid vma. The vma is stable for as long as the vma read lock is held.
+            vma: unsafe { VmaRef::from_raw(vma) },
+            _nts: NotThreadSafe,
+        })
+    }
+
     /// Lock the mmap read lock.
     #[inline]
     pub fn mmap_read_lock(&self) -> MmapReadGuard<'_> {

-- 
2.55.0.691.gc56d675ccc-goog

[PATCH v5 5/5] tcp: Remove mmap_lock fallback path

From: Suren Baghdasaryan <surenb@google.com>
Date: 2026-08-12 01:11:29

From: Dave Hansen <dave.hansen@linux.intel.com>

Previously, the per-VMA locking could fail in the face of writers
which necessitates a fallback to mmap_lock. The new
vma_start_read_unlocked() will wait for writers instead of failing.

Use the new helper. Wait for writers. Remove the fallback to mmap_lock.
The fallback removal does not affect NOMMU case because TCP_ZEROCOPY
is gated on CONFIG_MMU.

This really is a nice cleanup. It removes the need to pass the lock
state back and forth to find_tcp_vma().

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Lorenzo Stoakes <ljs@kernel.org>
Acked-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Tested-by: syzbot@syzkaller.appspotmail.com
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Liam R. Howlett <redacted>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: linux-mm@kvack.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Arve Hjønnevåg <arve@android.com>
Cc: Todd Kjos <tkjos@android.com>
Cc: Christian Brauner <christian@brauner.io>
Cc: Carlos Llamas <cmllamas@google.com>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: David Ahern <dsahern@kernel.org>
Cc: netdev@vger.kernel.org
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
 net/ipv4/tcp.c | 31 +++++++++----------------------
 1 file changed, 9 insertions(+), 22 deletions(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 455441f1b694..62defe70f3ce 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c

@@ -2167,27 +2167,18 @@ static void tcp_zc_finalize_rx_tstamp(struct sock *sk,
 }
 
 static struct vm_area_struct *find_tcp_vma(struct mm_struct *mm,
-					   unsigned long address,
-					   bool *mmap_locked)
+					   unsigned long address)
 {
-	struct vm_area_struct *vma = lock_vma_under_rcu(mm, address);
+	struct vm_area_struct *vma = vma_start_read_unlocked(mm, address);
 
-	if (vma) {
-		if (vma->vm_ops != &tcp_vm_ops) {
-			vma_end_read(vma);
-			return NULL;
-		}
-		*mmap_locked = false;
-		return vma;
-	}
+	if (!vma)
+		return NULL;
 
-	mmap_read_lock(mm);
-	vma = vma_lookup(mm, address);
-	if (!vma || vma->vm_ops != &tcp_vm_ops) {
-		mmap_read_unlock(mm);
+	if (vma->vm_ops != &tcp_vm_ops) {
+		vma_end_read(vma);
 		return NULL;
 	}
-	*mmap_locked = true;
+
 	return vma;
 }

@@ -2208,7 +2199,6 @@ static int tcp_zerocopy_receive(struct sock *sk,
 	u32 seq = tp->copied_seq;
 	u32 total_bytes_to_map;
 	int inq = tcp_inq(sk);
-	bool mmap_locked;
 	int ret;
 
 	zc->copybuf_len = 0;

@@ -2233,7 +2223,7 @@ static int tcp_zerocopy_receive(struct sock *sk,
 		return 0;
 	}
 
-	vma = find_tcp_vma(current->mm, address, &mmap_locked);
+	vma = find_tcp_vma(current->mm, address);
 	if (!vma)
 		return -EINVAL;

@@ -2315,10 +2305,7 @@ static int tcp_zerocopy_receive(struct sock *sk,
 						   zc, total_bytes_to_map);
 	}
 out:
-	if (mmap_locked)
-		mmap_read_unlock(current->mm);
-	else
-		vma_end_read(vma);
+	vma_end_read(vma);
 	/* Try to copy straggler data. */
 	if (!ret)
 		copylen = tcp_zc_handle_leftover(zc, sk, skb, &seq, copybuf_len, tss);

-- 
2.55.0.691.gc56d675ccc-goog

Re: [PATCH v5 2/5] binder: Make shrinker rely solely on per-VMA lock

From: Alice Ryhl <aliceryhl@google.com>
Date: 2026-08-12 10:46:35

On Tue, Aug 11, 2026 at 06:10:52PM -0700, Suren Baghdasaryan wrote:

 	return LRU_REMOVED_RETRY;
 
-err_invalid_vma:
 	mutex_unlock(&alloc->mutex);

With the err_invalid_vma label removed, this call to mutex_unlock() is
no longer reachable as it comes right after a 'return' statement.

Alice

Re: [PATCH v5 2/5] binder: Make shrinker rely solely on per-VMA lock

From: Suren Baghdasaryan <surenb@google.com>
Date: 2026-08-12 13:38:14

On Wed, Aug 12, 2026 at 3:46 AM Alice Ryhl [off-list ref] wrote:

On Tue, Aug 11, 2026 at 06:10:52PM -0700, Suren Baghdasaryan wrote:

quoted

      return LRU_REMOVED_RETRY;

-err_invalid_vma:
      mutex_unlock(&alloc->mutex);

With the err_invalid_vma label removed, this call to mutex_unlock() is
no longer reachable as it comes right after a 'return' statement.

Oh, darn! Carlos pointed it out in the previous version and I missed
it again. Sorry about that. I'll remove it, double-check I didn't miss
anything else and repost.
Thanks Alice!

Alice

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